During well drilling operations, a drill string is lowered into a wellbore. In some drilling operations, (e.g. conventional vertical drilling operations) the drill string is rotated. The rotation of the drill string provides rotation to a drill bit coupled to the distal end of a bottom hole assembly (“BHA”) that is coupled to the distal end of the drill string. The bottom hole assembly may include stabilizers, reamers, measurement-while-drilling (“MWD”) tools, logging-while-drilling (“LWD”) tools and other downhole equipment as known in the art. In some drilling operations, (e.g. if the wellbore is deviated from vertical), a downhole mud motor may be disposed in the bottom hole assembly above the drill bit to rotate the bit instead of rotating the drill string to provide rotation to the drill bit.
In some drilling operations, in order to pass through the inside diameter of upper strings of casing already in place in the wellbore, often times the drill bit will be of such a size as to drill a smaller gage hole than may be desired for later operations in the wellbore. It may be desirable to have a larger diameter wellbore to enable running further strings of casing and allowing adequate annulus space between the outside diameter of such subsequent casing strings and the wellbore wall for a good cement sheath. A borehole opener (“reamer”) may be included in the drill string to increase the diameter of the (“open”) borehole.
Some of the features in the drawings are enlarged to better show the features, process steps, and results.